This topic has probably been brought up before, but I've heard conflicting opinions on this, so I'm curious if anyone knows for sure roughly how much caffeine is released in the first steep vs second steep of sencha (or any green). I'm steeping a mid-steamed sencha for about a minute the first time around, and then 45 seconds for the second, and I've often wondered how much caffeine remains in the second steep. I assume it's different for a fukamushi, considering it's more broken up? I just want to make sure I'm not missing any of the caffeine. (Just kidding )

That blog is a pretty good source of information on Japanese green tea in general. Browse some of the entries, if you haven't come across it yet.

Oh and by the way, I think you might get better results (taste wise) by brewing the second infusion for a much shorter time than 45 s. Especially with deep or medium steeped teas, you can practically pour the tea right away without actually letting it sit in the water for any amount of time (like 1-10 s). That gives you a sweeter brew and will make the tea taste on subsequent infusions as well.However, you can do whatever you like best of course. Just a tip!